linux-kernel - Re: [PATCH 02/13] iommu: Move bus setup to IOMMU device registration

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Message-ID: <f72349ab-19d9-ed9f-28a7-6654fd5556cd@linux.intel.com>
Date:   Sat, 23 Apr 2022 16:51:23 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Robin Murphy <robin.murphy@....com>, joro@...tes.org,
        will@...nel.org
Cc:     iommu@...ts.linux-foundation.org, sven@...npeter.dev,
        robdclark@...il.com, m.szyprowski@...sung.com,
        yong.wu@...iatek.com, mjrosato@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, zhang.lyra@...il.com,
        thierry.reding@...il.com, vdumpa@...dia.com,
        jean-philippe@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/13] iommu: Move bus setup to IOMMU device registration

On 2022/4/23 16:37, Robin Murphy wrote:
> On 2022-04-23 09:01, Lu Baolu wrote:
>> Hi Robin,
>>
>> On 2022/4/19 15:20, Robin Murphy wrote:
>>> On 2022-04-19 00:37, Lu Baolu wrote:
>>>> On 2022/4/19 6:09, Robin Murphy wrote:
>>>>> On 2022-04-16 01:04, Lu Baolu wrote:
>>>>>> On 2022/4/14 20:42, Robin Murphy wrote:
>>>>>>> @@ -1883,27 +1900,12 @@ static int iommu_bus_init(struct bus_type 
>>>>>>> *bus)
>>>>>>>    */
>>>>>>>   int bus_set_iommu(struct bus_type *bus, const struct iommu_ops 
>>>>>>> *ops)
>>>>>>>   {
>>>>>>> -    int err;
>>>>>>> -
>>>>>>> -    if (ops == NULL) {
>>>>>>> -        bus->iommu_ops = NULL;
>>>>>>> -        return 0;
>>>>>>> -    }
>>>>>>> -
>>>>>>> -    if (bus->iommu_ops != NULL)
>>>>>>> +    if (bus->iommu_ops && ops && bus->iommu_ops != ops)
>>>>>>>           return -EBUSY;
>>>>>>>       bus->iommu_ops = ops;
>>>>>>
>>>>>> Do we still need to keep above lines in bus_set_iommu()?
>>>>>
>>>>> It preserves the existing behaviour until each callsite and its 
>>>>> associated error handling are removed later on, which seems like as 
>>>>> good a thing to do as any. Since I'm already relaxing 
>>>>> iommu_device_register() to a warn-but-continue behaviour while it 
>>>>> keeps the bus ops on life-support internally, I figured not 
>>>>> changing too much at once would make it easier to bisect any 
>>>>> potential issues arising from this first step.
>>>>
>>>> Fair enough. Thank you for the explanation.
>>>>
>>>> Do you have a public tree that I could pull these patches and try them
>>>> on an Intel hardware? Or perhaps you have done this? I like the whole
>>>> idea of this series, but it's better to try it with a real hardware.
>>>
>>> I haven't bothered with separate branches since there's so many 
>>> different pieces in-flight, but my complete (unstable) development 
>>> branch can be found here:
>>>
>>> https://gitlab.arm.com/linux-arm/linux-rm/-/commits/iommu/bus
>>>
>>> For now I'd recommend winding the head back to "iommu: Clean up 
>>> bus_set_iommu()" for testing - some of the patches above that have 
>>> already been posted and picked up by their respective subsystems, but 
>>> others are incomplete and barely compile-tested. I'll probably 
>>> rearrange it later this week to better reflect what's happened so far.
>>
>> I wound the head back to "iommu: Clean up bus_set_iommu" and tested it
>> on an Intel machine. It got stuck during boot. This test was on a remote
>> machine and I have no means to access it physically. So I can't get any
>> kernel debugging messages. (I have to work from home these days. :-()
>>
>> I guess it's due to the fact that intel_iommu_probe_device() callback
>> only works for the pci devices. The issue occurs when probing a device
>> other than a PCI one.
> 
> Yeah, I was wondering if that would be significant, since it's the only 
> driver that never registered itself for platform_bus_type so won't have 
> actually seen those calls before. I'm inclined to bodge that as below 
> for now, as long as it then works OK in terms of the rest of the changes.
> 
> Thanks,
> Robin.
> 
> ----->8-----
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 9fa1b98186a3..6e359f92ec00 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4565,6 +4565,10 @@ static struct iommu_device 
> *intel_iommu_probe_device(struct device *dev)
>       unsigned long flags;
>       u8 bus, devfn;
> 
> +    /* ANDD platform device support needs fixing */
> +    if (!pdev)
> +        return ERR_PTR(-ENODEV);
> +
>       iommu = device_to_iommu(dev, &bus, &devfn);
>       if (!iommu)
>           return ERR_PTR(-ENODEV);

I haven't seen any real ANDD platform devices, hence this works for me.

Best regards,
baolu